DESCRIPTION: Most of the ATP used for the different work performances of eucaryotic cells is derived from the metabolic pathways housed in mitochondria. This ancient organelle, believed to be a descendant of an earlier aerobic procaryote, has retained only a vestige of its original genetic information, most having been transferred to the nucleus of the host cell. The maintenance of functinal mitochondria in yeast and higher eucaryotic cells is governed by 30-40 genes resident in mitochondrial DNA and approximately 300 genes located in chromosomal DNA. Several large scale screens for respiratory defective strains of the yeast Saccharomyces cerevisiae, were carried out in prior grant periods. The mutants, comprising some 215 complementation groups, describe a wide range of different functions essential for expression of respiratory competent mitochondria. Most of the genes represented by the mutants have been cloned and sequenced. In many instances, the functions of the encoded products have been identified. Several goals will be pursued during the coming period. The assembly of the ATPase and bc1 complexes will be analyzed by both traditional biochemical methods and through studies aimed at gaining a more precise understanding of the functions carried out by novel gene products that affect late events in the assembly pathway. The second goal is to make use of the genes for the mitochondrial ribosomal proteins and aminoacyl-tRNA synthetases to clarify issues related to the regulation and evolution of these mitochondrial constituents. Finally, the analysis of the mutants collection will be completed. Hopefully, this will provide a genetic blueprint of mitochondrial morphogenesis and answer some of the still outstanding questions regarding the mechanisms insuring their continuity during cell growth and division.